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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 1. March 2012 
from October through March (average rainfall = 
919 mm. temperatures varied from 15.7 to 32.4 
°C) and a dry. cold season from April through 
September (average rainfall = 294 mm, temper¬ 
atures varied from 11.4 to 30.6 C). 
Study Species .—The Yellowish Pipit is a 
monomorphie passerine widely distributed in 
South America from western Panama south to 
Uruguay and Argentina (south to La Pampa and 
Buenos Aires). It inhabits grasslands, open C'er- 
rado. pastures, and cultivated lands often near 
water or marshes (Ridgely and Tudor 1994, Sick 
1997, Tyler 2004). The Yellowish Pipit is a 
common species, but data on its breeding biology 
are scattered and many aspects are poorly docu¬ 
mented. Data on incubation and nestling periods, 
breeding phenology, and parental care are present¬ 
ed here for the first time. 
Field Procedures. -Wc conducted systematic 
nest searches from July to January during three 
breeding seasons (2008, 2009, and 2010). We 
searched for nests at least three times per week by 
covering 1 km of each margin of the Sorocaba 
River and Lhe entire adjacent park. Nests were 
located by following adults in their territories 
when they were carrying nest material or feeding 
young, and were checked every 1-3 days. We 
used metal calipers accurate to ± 0.01 mm to 
measure nests and eggs, and a spring scale 
accurate to ± 0.1 g to weigh eggs. 
The incubation period was from the first day 
of incubation to the day before hatching, and 
nestling period was from hatching day to the day 
before Hedging. Observations were performed 
daily during the laying stage, and we could detect 
females that began incubation before and after the 
set of eggs was complete. We also checked if eggs 
were warm to detect Lite beginning of incubation. 
We did not touch or handle young to avc 
shortening the nestling period (Skutch 194‘ 
Clutch initiation dates were obtained from ne: 
found in die construction stage (i.e.. we observ 
the first egg in die nests) (n = 15), and by bac 
dating for nests for which hatching or fledgi 
dates were known, based on mean incubation u 
nestling periods (// = 12 ), 
We estimated lhe frequency at which adu 
>i'° WM thc Pulton 
<W. ns well 
nestling perLiCThr^f "T " 
These observations were made early in the 
morning (0600-0900 hrs). 
We assumed predation to have occurred when 
eggs or nestlings younger than fledging age iwith 
poorly developed feathers) disappeared from a 
nest or when eggs or young were found partial!) 
eaten near nests. Abandonment was considered 
when adults were not seen near the nests during 
the observation sessions for at least 3 consecutive 
days, and eggs were cold (Pletschet and Kelly 
1990). 
Statistical Analysis .—We used the maximum 
likelihood method implemented in Program 
MARK, Version 6.1 (White and Burnham 1999. 
Dinsmore et al. 2002) to estimate nest success 
based on 20 nests for which information met the 
criteria for Program MARK (pooling all years). 
We calculated daily survival rate (DSR) using the 
null model of constant DSR. S(.), which is similar 
to that of Mayfield (1961). The cumulative 
probability of overall nest success was estimated 
by raising DSR to the power corresponding to the 
mean duration of the nesting cycle obtained in our 
study (incubation + nestling periods). We evalu¬ 
ated a set of three Program MARK candidate DSR 
models that used continuously varying covariales: 
(1) Stnest age) (number of days since incubation 
onset date). (2) S(date) (date within the breeding 
season), and (3) their combinations. St date + nest 
age). These models were compared to the null 
model of constant DSR using Akaike's Informa¬ 
tion Criterion for small samples (AIQ. The 
model with the lowest AIC C value was considered 
the best tit of the data, but models with AAIC ( . - 
2 were also considered as presenting substantial 
support for explaining the data (Burnham mid 
Anderson 1998). Akaike weight Ov) was used to 
measure the relative support for each candidate 
model. We used logit-link function to convert all 
DSR values to an interval between 0 and one 
Model-averaged estimates of DSR were calculat¬ 
ed for early (arbitrarily defined as the 10 th day 
after the encounter of the first nest), middle t.50tl' 
day), and late (90th day) breeding season. Erf 
laying stage was not considered in our DSR 
analyses due to lack of parental activities during 
this stage. 
The clutch size of Yellowish Pip 11 V ' J ' 
compared to populations of: Buff-bellied (Ad^l 
iean) Pipit (A. rubescens) from Wyoming. C- 
(Verbeek 1970); Sprague's Pipit (A. iprW u 
from southern Saskatchewan, Canada P v,s 
2003, 2009), and England and Northern Europe 
